1. Field of the Invention
This invention relates to a video additive information identifying device, and particularly to a device for identifying video additive information representing a frame mode of a video signal whose aspect ratio is converted.
2. Description of Related Art
Recently, a television receiver usable for a Hi-vision broadcasting of 16:9 aspect ratio has been practically used, and also practical use of video equipments which are suitable for a wide image of 16:9 aspect ratio has been promoted even in an NTSC system which is a conventional television system.
In addition, in those equipments which are connected to the above video equipments, equipments each adopting currently-used aspect ratio of 4:3 and other types of equipments adopting aspect ratio of 16:9 have been intermixingly used, and connected to monitor terminals of Hi-vision image receivers.
In these cases, an identification information on video information, that is, a video ID is required to enable a user to freely operate these equipments without inconvenience. In order to satisfy this requirement there has been utilized a method in which the identification information is inserted as a video additive information into a vertical blanking period of a video signal.
A Hi-vision signal, particularly, is converted to an NTSC signal using a MUSE-NTSC converter for example. In this case, the video additive information, that is, the video ID signal is inserted into the converted NTSC signal at its vertical blanking period because the Hi-vision signal has originally 16:9 aspect ratio.
FIG. 1 shows a signal waveform of an example of the video ID signal. In this video ID signal, a reference signal having 70IRE amplitude and 20-bit digital signal data having 70IRE or 0IRE amplitude are arranged at an effective video portion of one horizontal line, and an identification signal is coded and inserted to the 20-bit digital signal data. A clock frequency is set to f.sub.sc /8.apprxeq.447 KHz, and 20th and 28th lines of the vertical blanking period are selected for transmission.
In a video display equipment for reproducing and displaying a video image from a video signal source having such video additive information, such as a television receiver, the video additive information is identified, and an optimum reproducing and displaying condition can be automatically set on the basis of the identification result.
In general, a video display equipment such as a television receiver has an input circuit which is usable for plural video signal sources. When a signal source having the information as described above is used as an input source, in a usual case a signal system for each video input is individually equipped with an identifying circuit for a video additive information, for example, a wide ID to make an identification.
According to the construction of the identifying circuit for the video additive information as described above, the input circuit for plural video signal sources requires plural video additive information identifying circuits which are suitable for the signal video signals, respectively. Therefore, the conventional device has a problem that the circuit construction is complicated, and the cost thereof is high.